This invention relates to automatic analysis apparatus and more particularly, to such apparatus which includes a colorimeter flow cell device for the quantitative colorimetric analysis of a fluid stream in respect to an ingredient thereof. Such apparatus is shown and described in U.S. Pat. No. 3,804,593. The apparatus may be used for the chemical analysis of a stream of a series of individual clinical or industrial samples, or for monitoring a continuous sample-liquid stream, for example but without limitation, in an industrial plant to monitor a manufacturing process, a waste stream, etc.
Heretofore, flow cells of tubular glass, with sight passageways, having at their respective ends bent or curved liquid inlet and outlet portions, have been constructed by glass-blowing or lamp-working techniques. Such a flow cell is disclosed in U.S. Pat. No. 3,241,432. A flow cell formed in this manner may exhibit good laminar flow characteristics. However the bent or curved glass at the respective ends of the cell passageway through which light is directed often fails to exhibit optimum optical qualities. For example, some light from the source may be absorbed in the end walls or refracted therefrom instead of passing substantially axially along the cell passageway. In addition, optical problems have resulted in part because of lack of uniformity in the curved end walls of such a flow cell, and lack of uniformity of one cell with reference to another.
Attempts have been made to improve the optical qualities of a flow cell by the construction of flat end windows for the sight passageway, which windows have been constructed and assembled so as to have their inner and outer surfaces parallel and lying in planes normal to the axis of the tubular body forming the sight passageway. Such a flow cell is disclosed in U.S. Pat. No. 3,345,910. While this construction lessened the afore mentioned refraction problem which resulted from the curved or bent liquid inlet and outer portions of the cell type first described above, and resulted in better uniformity in the end walls of such a flow cell, it did not solve the problem of effectively limiting loss of light from within the end windows such as by transmission directly to the material of the cell body at the interfaces of the latter with the windows. The end windows of this flow cell are glass as is the body of the flow cell. It has been found in the use of such windowed flow cells that stagnant regions tend to form in the sight passageway. Particulate foreign matter and very fine bubbles, considerably smaller than the passageway, tend to accumulate in these regions. It has been noted that this stagnation occurs particularly in the ends of the sight passageways, next to the windows. More specifically, it has been observed that dirt and small bubbles tend to collect at the bottoms of the windows. It is believed by some that this accumulation is at its greatest at the window near the liquid outlet from the sight passageway. Liquid in such analysis systems is normally pulsed, and when such pulsations occur in a windowed flow cell, such as described above, dirt and bubbles tend to spurt upwardly from the bottom of the sight passageway in a direction across the windows. This particulate foreign matter and small bubbles tend to obscure such a sight passageway, particularly the windows thereof. This results in what is known as optical noise in the signals transmitted from the flow cell to the light detector, which in turn effects a nonlinear affect in the operation of an analysis system such as that disclosed in U.S. Pat. No. 3,804,593.
Prior art flow cells such as illustrated in U.S. Pat. No. 3,583,817, have been designed to overcome the problems that have occured previously when the inner surfaces of the end windows made a perpendicular angle with respect to the axis of the passageway of the flow cell.